14,294 research outputs found
Massive particle with torsion and conformal mechanics
The consequences of coupling of the torsion (highest curvature) term to the
Lagrangian of a massive spinless particle in four-dimensional space-time are
studied. It is shown that the modified system remains spinless and possesses
extended gauge invariance. Though the torsion term does not generate spin, it
provides the system with a nontrivial mass spectrum, described by
one-dimensional conformal mechanics. Under an appropriate choise of
characteristic constants the system has solutions with a discrete mass
spectrum.Comment: 9 pages, revised version accepted in Phys.Lett.
Cosmological Constant from Decoherence
We address the issue why a cosmological constant (dark energy) possesses a
small positive value instead of being zero. Motivated by the cosmic landscape
picture, we mimic the dark energy by a scalar field with potential wells and
show that other degrees of freedom interacting with it can localize this field
by decoherence in one of the wells. Dark energy can then acquire a small
positive value. We also show that the additional degrees of freedom enhance the
tunneling rate between the wells. The consideration is performed in detail for
the case of two wells and then extended to a large number of wells.Comment: 39 pages, 2 figures, final versio
Fiber waveguide sensors for intelligent materials
This report, an addendum to the six month report submitted to NASA Langley Research Center in December 1987, covers research performed by the Fiber and Electro-Optics Research Center (FEORC) at Virginia Tech for the NASA Langley Research Center, Grant NAG1-780, for the period from December 1987 to June 1988. This final report discusses the research performed in the following four areas as described in the proposal: Fabrication of Sensor Fibers Optimized for Embedding in Advanced Composites; Fabrication of Sensor Fiber with In-Line Splices and Evaluation via OTR methods; Modal Domain Optical Fiber Sensor Analysis; and Acoustic Fiber Waveguide Implementation
Organic Farming Scenarios: Operational Analysis and Costs of implementing Innovative Technologies
The objective of this study has been to design a number of farm scenarios representing future plausible and internally consistent organic farming enterprises based on milk, pig, and plant production and use these farm scenarios as the basis for the generation of generalised knowledge on labour and machinery input and costs. Also, an impact analysis and feasibility study of introducing innovative technologies into the organic
production system has been invoked.
The labour demand for the production farms ranged from 61 to 253hha1 and from 194 to 396hLU1 (LU is livestock units) for work in the animal houses. Model validation results showed that farm managerial tasks amount to 14â19% of the total labour requirement. The impact of introducing new technologies and work methods related to organic farming was evaluated using two innovative examples of weed control: a
weeding robot and an integrated system for band steaming. While these technologies increased the capital investment required, the labour demand was reduced by 83â85% in sugar beet and 60% in carrots, which would improve profitability by 72â85% if fully utilised. Profitability is reduced, if automation efforts result in insufficient weed removal compared to manual weeding. Specifically, the benefit gained by robotic weeding
was sensitive to the weed intensity and the initial price of the equipment, but a weeding efficiency of under 25% is required to make it unprofitable.
This approach demonstrates the feasibility of applying and testing operational models in organic farming systems in the continued evaluation and documentation of labour and machinery inputs
Scalar-tensor cosmological simulations
We present -body cosmlogical simulations in the framework of the Newtonian
limit of scalar-tensor theories of gravity. The scalar field is described by a
modified Helmholtz equation with a source that is coupled to the standard
Poisson equation of Newtonian gravity. The effective gravitational force is
given by two contributions: the standard Newtonian potential plus a Yukawa
potential stemming from massive scalar fields. In particular, we consider
simulations of CDM models and compute the density and velocity
profiles of the most massive groups found at z=0.Comment: 6 pages, 6 figures. Recent Developments in Gravitation and
Experimental Physics: 3rd Mexican Meeting of Mathematical and Experimental
Physics. Edited by A. Macias, C. Laemmerzahl, and A. Camacho. (American
Institute of Physics, 2008). Pag. 30
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